Blood can be fractionated, and the different fractions of the blood are useful for different medical needs. Under the influence of gravity or centrifugal force, blood spontaneously separates into three layers. At equilibrium, the top low-density layer is a straw-colored clear fluid called plasma. Plasma is a water solution of salts, metabolites, peptides, and many proteins ranging from small (insulin) to very large molecules (complement components).
The bottom, high-density layer is a deep red viscous fluid comprising anuclear red blood cells (erythrocytes) specialized for oxygen transport. The red color is imparted by a high concentration of chelated iron or heme that is responsible for the erythrocytes' high specific gravity. The relative volume of whole blood that consists of erythrocytes is called the hematocrit, and in normal human beings this can range from about 37% to about 52% of whole blood.
The intermediate layer is the smallest, appearing as a thin white band above the erythrocyte layer and below the plasma layer; this is called the buffy coat. The buffy coat itself has two major components, nucleated leukocytes (white blood cells) and anuclear smaller bodies called platelets (or thrombocytes). Leukocytes confer immunity and contribute to debris scavenging. Platelets seal ruptures in blood vessels to stop bleeding, and deliver growth and wound healing factors to a wound site. Slower speed centrifugation or shorter duration centrifugation permits separation of erythrocytes and leukocytes from plasma, while the smaller platelets remain suspended in the plasma, resulting in platelet rich plasma (PRP).
U.S. Pat. No. 5,585,007 identifies methods for making plasma concentrates from whole blood for use in wound healing and as a tissue sealant. This patent is hereby incorporated by reference in its entirety. This device, designed for placement in a medical laboratory or surgical amphitheatre, uses a disposable cartridge for preparing tissue sealant. The device was particularly applicable for stat preparations of autologous tissue sealants. Preparation in the operating room of 5 ml of sealant from 50 ml of patient blood required less than 15 minutes and only one simple operator step. There was no risk of tracking error because preparation could take place in the operating room during the surgical procedure. Chemicals added could be limited to anticoagulant (e.g., citrate) and calcium chloride. The disposable cartridge could fit in the palm of the hand and was hermetically sealed to eliminate possible exposure to patient blood and to ensure sterility. Adhesive and tensile strengths of the product were comparable or superior to pooled blood fibrin sealants made by precipitation methods. Use of antifibrinolytic agents (such as aprotinin) was not necessary because the tissue sealant contained high concentrations of natural inhibitors of fibrinolysis from the patient's blood.
This device used a new sterile disposable cartridge with the separation chambers for each run. Since the device was designed to be used in a normal medical setting with ample power, the permanent components were designed for long-term durability, safety and reliability, and were relatively heavy, using conventional centrifuge motors and accessories.
Small, self-contained centrifugal devices for obtaining platelet concentrates from blood are described in commonly assigned, copending application Ser. No. 10/394,828 filed Mar. 21, 2003, the entire contents of which are hereby incorporated by reference. This device separates blood into erythrocyte, plasma and platelet layers and selectively removes the platelet layer as a platelet concentrate, that is, platelets suspended in a minimal amount of plasma. The plasma fraction, being in an unconcentrated form, is not effective as a hemostat or tissue adhesive.
Platelet rich plasma is a concentrated platelet product that can be produced from whole blood through commercially available systems, resulting in varying levels of platelet concentration. Platelets play a crucial role in the signaling cascade of normal wound healing. Activated platelets release the contents of their α-granules resulting in a deposition of powerful growth factors such as platelet derived growth factor (PDGF), transforming growth factor β-(TGF-β), vascular endothelial growth factor (VEGF), and epidermal growth factor (EGF). PRP has been used in many different clinical applications, demonstrating the effectiveness and importance of the product for a variety of medical procedures. For example, percutaneous application of PRP to patients with severe lateral epicondylitis, or tennis elbow, resulted in improved elbow function and reduced pain. Early maturation of bony fusion was observed when platelet concentrate was used during lumbar spinal fusions. Chronic diabetic foot ulcers treated with PRP achieved increased healing rates compared to the control group receiving standard care. Studies by Bhanot el at show decreased formation of hematoma and seroma, decreased postoperative swelling, and improved healing time for plastic surgeries that included PRP in the treatment. Further, during dental surgeries, the use of PRP has improved bone regeneration around implants.
PRPs have demonstrated numerous clinical benefits to patients. There are many devices on the market that concentrate platelets to differing levels. At this time, it is unclear the amount of platelets that is most efficient for each surgical application. Concentrations of at least 1,000×103 platelets/μL are recommended. The system described in copending application Ser. No. 10/394,828 can provide platelets up to 8 time baseline concentration, and the normal human platelet range is 200×103 platelets/μL to 400×103 platelets/μL. This means a highly effective concentrate in a range of 1,600×103 platelets/μL to 3,200×103 platelets/μL.
However, the PRP products of the prior invention, while achieving greatly increased platelet concentrations, did not have tissue sealant and hemostatic properties needed for many surgeries. The platelet-free plasma concentrates, while they were excellent sealants and hemostats, did not provide the healing properties of platelets.